需要对 iOS 中的 @property/@synthesize 进行解释
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Need explanation on @property/@synthesize in iOS
提问by HpTerm
Not a complete noob I am quite new to iOS programming and to Ojbective-C. I mainly come from a background of C (DSP, Microcontrollers), Delphi XE2/Pascal , Visual Basic and Java (desktop and Android apps).
不是一个完整的菜鸟我对 iOS 编程和 Ojbective-C 很陌生。我主要来自 C（DSP、微控制器）、Delphi XE2/Pascal、Visual Basic 和 Java（桌面和 Android 应用程序）的背景。
I mainly learned Cocoa with the book "Beginning iOS 5 Development", from Apress.
我主要是通过 Apress 的“Beginning iOS 5 Development”一书学习 Cocoa。
Recently I watched videos of the WWDC 2012 and went through some of their sample code, and I must say that I am confused of what is the proper way of writing my apps and more specifically with the @property/@synthesize words.
最近我观看了 WWDC 2012 的视频并浏览了他们的一些示例代码，我必须说我很困惑什么是编写我的应用程序的正确方法，更具体地说是 @property/@synthesize 词。
In the book most (not to say all) of the sample code uses to define a property as for example
书中大部分（不是全部）示例代码用于定义一个属性，例如
ViewController.h
@property (strong, nonatomic) NSMutableArray *list;
ViewController.m
@synthesize list;
then all the code access synthesize list with
然后所有的代码访问合成列表
self.list
or even simply
甚至干脆
list
Now in every WWDC code sample I read I see that programmers define a property but then, in the .m file they do things like
现在，在我阅读的每个 WWDC 代码示例中，我看到程序员定义了一个属性，但是，在 .m 文件中，他们执行了类似的操作
@synthesize list = _list;
and access sometimes
有时访问
self.list
or
或者
_list
I am confused. What is the correct practice ? As Apple programmers all use underscore I think I should do it that way but why the book did not ? Is there a difference between list and _list ? And more over, as I am in the same object why sometime use self.list and sometimes list/_list.
我很迷惑。什么是正确的做法？由于 Apple 程序员都使用下划线，我想我应该这样做，但为什么这本书没有呢？list 和 _list 之间有区别吗？更重要的是，因为我在同一个对象中，为什么有时使用 self.list 有时使用 list/_list。
Sometimes they don't use @synthesize, I assume it's when they want to re-write their own accessors and mutators (which is never my case up to now).
有时他们不使用@synthesize，我认为这是他们想要重写自己的访问器和修改器的时候（到目前为止，这从来不是我的情况）。
I have read here and there on the web but nothing was clear enough to set my mind right, so I count on StackOverflow to bring light here.
我已经在网络上到处阅读，但没有任何内容足以让我的想法正确，所以我指望 StackOverflow 在这里带来光明。
Last but not least I prefer and answer based on current iOS 6 best practice/programming technique. Useless to tell me how to do it correctly in older iOS.
最后但并非最不重要的是，我更喜欢并根据当前的 iOS 6 最佳实践/编程技术进行回答。告诉我如何在较旧的 iOS 中正确地做到这一点毫无用处。
采纳答案by Warren Burton
There is no correct way. There is only your preferred style.
没有正确的方法。只有你喜欢的风格。
The lastest compilers do an implicit synthesise on the property declaration.
最新的编译器对属性声明进行了隐式综合。
@synthesize list = _list;.
@synthesize list = _list;.
Nothing is ever written in your code. It just happens.
您的代码中从未写过任何内容。它只是发生。
However that doesnt stop you doing this explicitly.
但是，这并不能阻止您明确地执行此操作。
@synthesize list = somethingelse;
@synthesize list = somethingelse;
So when you ask for a pointer to listvia the accessor (self.list) you will get a pointer to somethingelse
因此，当您list通过访问器 ( self.list)请求指向的指针时，您将获得指向somethingelse
In most cases NSMutableArray *thing = self.listis equivalent to NSMutableArray *thing = somethingelse
在大多数情况下NSMutableArray *thing = self.list相当于NSMutableArray *thing = somethingelse
And just because Apple uses a style doesn't mean that you have to do it. Each company usually has their own coding style.
仅仅因为 Apple 使用一种风格并不意味着你必须这样做。每个公司通常都有自己的编码风格。
The main problem with using @synthesize list;is that it poses the risk that you can write either
使用的主要问题@synthesize list;是它带来了您可以编写的风险
self.list = thingor list = thing.
self.list = thing或list = thing。
The former uses the sythesised setList:accessor while the latter doesn't and put the risk of related bugs in your code , though its not as bad with ARCas you dont get leaks happening for strongproperties.
前者使用合成的setList:访问器，而后者不使用并在您的代码中放置相关错误的风险，尽管它并不ARC像您不会发生strong属性泄漏那样糟糕。
What ever style you use, keep it consistent and be aware of the effects of using an ivar directly list = thingas compared to using its accessor self.list = thing
无论你使用什么风格，保持一致并注意直接使用 ivarlist = thing与使用其访问器相比的效果self.list = thing
回答by Phillip Mills
This is a language feature that has had its usage evolve rapidly over the past few years, which explains the various forms. With the most recent tools, you can choose to ignore @synthesizeand have things work reasonably.
这是一种语言特性，其用法在过去几年中迅速发展，这解释了各种形式。使用最新的工具，您可以选择忽略@synthesize并让事情合理地工作。
The default behavior in that case produces the same effect as @synthesize list = _list;.
这种情况下的默认行为产生与 相同的效果@synthesize list = _list;。
